Wireless communication devices such as terminals are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals and/or Mobile Stations (MS). These terms will be used interchangeably hereafter.
Wireless communication devices are enabled to communicate wirelessly in a wireless or cellular communications network or a wireless communication system, sometimes also referred to as a cellular radio system or a cellular network. The communication may be performed e.g. between two wireless communications devices, between a wireless communications device and a regular telephone and/or between a wireless communications device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the wireless communications network.
Access network nodes, also referred to as access nodes, such as base stations, communicate over the air interface operating on radio frequencies with the wireless communication devices within range of the access network nodes. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the access network node to the wireless communication devices. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the wireless communication devices to the access network node.
Further, each access network node may support one or several communications technologies or radio interfaces also referred to as Radio Access Technologies (RAT). Examples of wireless communication technologies are New Radio (NR), Long Term Evolution (LTE), Universal Mobile Telecommunications System (UMTS) and Global System for Mobile communications (GSM).
In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for networks and investigate various topics, such as enhanced data rate and radio capacity.
It is expected that in a near future, the population of Cellular IoT (Internet of Things) devices, such as wireless communication devices, will be very large. Various predictions exist, among which may be mentioned document 3GPP TR 45.820 V13.1.0, “Cellular system support for ultra-low complexity and low throughput Internet of Things (CIoT)” that assumes >60000 IoT devices per square kilometer, and document 3GPP TR 38.913 v 14.0.0, “Study on Scenarios and Requirements for Next Generation Access Technologies” that assumes 1000000 devices per square kilometer. A large fraction of these IoT devices are expected to be stationary, e.g., gas and electricity meters, vending machines, etc. EC-GSM-IoT and NB-IoT are two standards for Cellular IoT specified by 3GPP TSG GERAN and TSG RAN.
Positioning
Positioning enhancements for GERAN have been discussed, for example in document RP-161260, “New Work Item on Positioning Enhancements for GERAN”, source Ericsson LM, Orange, MediaTek Inc., Sierra Wireless, Nokia. RAN #72. One candidate method for realizing improved accuracy when determining a position of a mobile station is Timing Advance (TA) multilateration which relies on establishing a position of the MS based on TA values in multiple cells. See for example document RP-161034, “Positioning Enhancements for GERAN—introducing TA trilateration”, source Ericsson LM. RAN #72.
A proposal based on a similar approach to support positioning of NarrowBand internet-of Things (NB-IoT) mobiles has been made in document 3GPP TR 38.913 v 14.0.0, “Study on Scenarios and Requirements for Next Generation Access Technologies”.
TA is a measure of the propagation delay between a base transceiver station (BTS) and the MS. The TA may be defined as the propagation delay between the base station and the wireless device and back to the base station again, i.e. TA=PDL+PUL where PDL is the downlink propagation delay and PUL is the uplink propagation delay. Since the speed by which radio waves travel is known, the distance between the BTS and the MS may be derived. Further, if multiple BTSs each measure a respective TA to the same MS and the positions of these BTSs (i.e. longitude and latitude) are known, the position of the MS may be derived. Measurement of TA requires that the MS synchronizes to each BTS used during the Multilateration procedure and transmits a signal time-aligned with the timing of each BTS (as estimated by the MS). The BTS then measures the time difference between its own time reference, and the timing of the signal received from the MS on each of the BTS. As mentioned above this time difference is equal to two times the propagation delay between the BTS and the MS, one propagation delay of the BTS's synchronization signal to the MS, plus one equally large propagation delay of the signal transmitted by the MS back to the BTS, and is used to determine a BTS specific TA value.
Once a set of TA values are established, the position of the MS may be derived through so called Multilateration where the position of the device is determined by the intersection of a set of hyperbolic curves associated with each BTS, see FIG. 1. The calculation of the position of the MS is typically carried out by a positioning node, such as an Serving Mobile Location Center (SMLC), which implies that all of the derived timing advance and corresponding cell identity information is to be sent to the positioning node that initiated the procedure, i.e. the serving SMLC.
Herein the following definitions are used:                Foreign BTS: A BTS associated with a first Base Station System (BSS) that uses a positioning node that is different from the positioning node used by a second BSS that manages the cell serving the MS when the positioning procedure is initiated. In this case the derived timing advance information and identity of the corresponding cell are relayed to the serving positioning node using the core network, since in this case the first BSS has no context for the MS.        Local BTS: A BTS associated with a first BSS that is different than the second BSS that manages the cell serving the MS when the positioning procedure is initiated. However, the first BSS associated with the local BTS uses the same positioning node as the second BSS. In this case the derived timing advance information and identity of the corresponding cell are relayed to the serving positioning node using the core network, i.e. in this case the first BSS has no context for the MS.        Serving BTS: A BTS associated with the second BSS that manages the cell serving the MS when the positioning procedure is initiated. In this case the derived timing advance information and identity of the corresponding cell are sent directly to the serving positioning node, i.e. in this case the BSS has a context for the MS.        Serving SMLC node: The SMLC node that commands a MS to perform the Multilateration procedure, i.e. it sends an RRLP Multilateration Request to the MS. The RRLP Multilateration Request may be tunneled to the MS via the serving BSS.        Serving BSS: The BSS associated with the serving BTS, i.e. the BSS that has context information for the Temporary Logical Link Identifier (TLLI) corresponding to the MS for which the Multilateration procedure has been triggered. The TLLI provides the signaling address used for communication between the user equipment and the SGSN (Serving GPRS Support Node) and is specified in 3GPP specification 23.003        Non-serving BSS: A BSS associated with a Foreign or Local BTS, i.e. a BSS that does not have context information for the TLLI corresponding to the MS for which the Multilateration procedure has been triggered.        